<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .font-size .one{
            font-size: 30px;
        }
        .font-size .two{
            font-size: 10px;
        }
    </style>
</head>
<body>
    <div class="font-size">
        <div class="one">
            大大大
        </div>
        <div class="two">
            小小小
        </div>
    </div>
</body>
</html>